Nathaniel Leonard

Impact of transition metal on nitrogen retention and activity of iron–nitrogen–carbon oxygen reduction catalysts

Iron based nitrogen doped carbon (FeNC) catalysts are synthesized by high-pressure pyrolysis of carbon and melamine with varying amounts of iron acetate in a closed, constant-volume reactor. The optimum nominal amount of Fe (1.2 wt%) in FeNC catalysts is established through oxygen reduction reaction (ORR) polarization. Since the quantity of iron used in FeNCs is very small, the amount of Fe retained in FeNC catalysts after leaching is determined by UV-VIS spectroscopy. As nitrogen is considered to be a component of active sites, the amount of bulk and surface nitrogen retention in FeNC catalysts are measured using elemental analysis and X-ray photoelectron spectroscopy, respectively. It is found that increasing nominal Fe content in FeNC catalysts leads to a decreased level of nitrogen retention. Thermogravimetric analysis demonstrates that increasing nominal Fe content leads to increased weight loss during pyrolysis, particularly at high temperatures. Catalysts are also prepared in the absence of iron source, and with iron removed by washing with hot aqua regia post-pyrolysis. FeNC catalysts prepared with no Fe show high retained nitrogen content but poor ORR activity, and aqua regia washed catalysts demonstrate similar activity to Fe-free catalysts, indicating that Fe is an active site component.

Effect of pyrolysis pressure on activity of Fe–N–C catalysts for oxygen reduction

Iron and nitrogen doped carbon, Fe–N–C, catalysts are synthesized by high pressure pyrolysis of Ketjenblack carbon, melamine and iron acetate precursor mixture in a closed, reusable scale-up stainless steel reactor. The effects of precursor loading with constant precursor ratios on obtained pressure, nitrogen retention and oxygen reduction reaction (ORR) activities are studied. The results indicate that higher precursor loading increases the gas phase pressure and improves nitrogen retention and ORR activity. Furthermore, a relationship is found between active site density, nitrogen retention and pressure that suggests that the limiting reaction may be an adsorption process driven via high pressure of volatile intermediates from the melamine.

Rotating Ring-Disk Study of Metal-Nitrogen-Carbon Catalyst Prepared by High Pressure Pyrolysis

The need for less expensive oxygen reduction (ORR) catalysts has impeded commercialization of low temperature fuel cells for transportation applications. Metal/nitrogen/carbon (MNC) electrocatalysts represent promising non-precious materials that catalyze ORR (13). Preparation of MNC electrocatalysts involves the combination of metal and nitrogen components immobilized in a conductive carbon matrix by the pyrolysis of precursor materials. In the present work, the kinetics of a MNC catalyst was characterized with rotating ring-disk electrode (RRDE) studies. The results were analyzed with existing kinetic models.